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134 Cards in this Set
- Front
- Back
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State TWO common examples of the beneficial effects of the chemical effects of electric current flow?
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Batteries or cells
- electroplating - electrolytic refining |
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State TWO common examples of the beneficial effects of the chemical effects of electric current flow? |
Batteries or cells - electroplating - electrolytic refining |
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State FIVE common examples of the beneficial effects of the magnetic effect of electric current flow? |
Electromagnetic devices. - measuring instruments - motors and generators - relays - transformers - contactors |
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state THREE common examples of the non beneficial effects of the magnetic effect of electric current flow? |
Magnetic stresses. - magnetic interference - hysteresis loss - Eddy current loss |
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state the main application of the beneficial effect of the thermal effect of electric current flow? |
heating elements |
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state TWO common effects of the non beneficial effects of electric current flow? |
- Power losses in machines - heating in cables |
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what is meant by the term electrolyte? |
an electrolyte is a liquid that conducts electricity |
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what conditions can result in electrolytic corrosion, as reffered in AS/NZS 3000 5.5.5.3? |
dissimilar metals joined in the pressence of an electrolyte (electrolytic corrosion) and effects of moisture |
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what are FIVE of the most dangerous effects of a high electric current passing through the human body? |
- electrocution - stop breathing - stop heart - ventricular defibrillation - severe burns |
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what is the lowest approximate value of electric current that is considered dangerous to pass through a human body? |
20 - 30mA (approximately) |
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List SIX factors which effect the severity of an electric shock. |
- voltage value - current value - path of current through the body - duration of contact - body resistance - point on cardiac cycle |
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which part of the body is effected by ventricular fibrilation? |
the heart |
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what are the THREE basic parts of any electrical cirtuit?
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voltage sourceconductors for carrying currentand a load that uses electricity
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typically, electrical circuits can consist of THREE basic components and TWO additional ones. what are they?
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basicvoltagesourceloadswitch protective device
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what is the purpose of a fuse or a circuit breaker in an electrical circuit?
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to automatically disconect the supply in case of a short circuit to earth or between active and neutral (protects equipment, not people)
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What is the approximate current that will trip a 10A circuit breaker?
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14.5A (1.45 x rating B3.2.1)
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What essential safety precaution must be taken before attempting to replace a fuse or reset a circuit breaker?
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Isolate the supply
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What is the name of the most common type of cartridge fuse used for high voltage circuits?
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High Rupturing Capacity fuse (HRC)
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what electrical value stays the same in all parts of a series circuit? |
Current |
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what electrical value stays the same in all parts of a parallel circuit? |
Voltage |
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state Kirchhoff's voltage law |
the sum of the potential differences must be equal to the total voltage in a series circuit |
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state Kichhoff's current law |
the sum of the current flowing towards a junction equals the sum of the currents flowing away from that junction |
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Ohm's Law |
I = V/R or V = IR |
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what effect would it have on the line current in a parallel resistive circuit, if one of the resistors was open circuited? |
the current would go down |
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formula to calculate total resistance in a resistive parallel circuit |
1/Rt = 1/R1 + 1/R2 + 1/R3 + ...
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what condition is necessary for a voltage to be induced in a conductor by a magnetic field? |
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how much voltage is induced in a conductor when it is moved in a parallel direction to magnetic lines of flux? |
0v. A voltage is only induced if the conductor crosses the lines of flux |
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a conductor loop is rotated uniformly withing a two pole magnetic field, at what point is the maximum voltage induced? |
when the loop is cutting the lines of flux at 90 degrees. |
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list FOUR values of alternating current |
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Peak voltage |
voltage value at the top of the sine wave |
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Vdc = |
Vdc = Vpeak x 0.707 |
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what value of a.c. do most standard instruments measure? |
RMS (root mean square) |
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what type of a.c. waveform does single phase alternator produce? |
a sinusoidal waveform |
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what is the phase displacement for waveforms in a three phase distribution system? |
120 degrees |
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how does a ammeter fit into a single phase a.c. circuit? |
in series with the load |
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how does a voltmeter fit into a single phase a.c. circuit? |
in parallel to the load being tested |
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how does a watmeter fit into a single phase a.c. circuit? |
in series and in parallel to the load being tested |
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Equation for Power Factor in single phase |
PF = P(W) / VA |
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what causes a lagging power factor |
an inductive circuit |
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what causes a leading power factor |
a capacitive circuit |
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CIVIL |
in a Capacitor, the I leads the V, whereas, the V leads the I in an L: inductor. |
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three phase Power Factor equation |
PF = cos(?) = P(w) / root3 x V x I |
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name FIVE types of 3 phase current limiting motor starters |
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what are three of the most likely causes of overheating of a typical 3 phase squirrel cage induction motor on load? |
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what type of load requires a fuse with a high rupturing 'slow-blow' capability? |
electric motors with a high 'in-rush' starting current |
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name the protection device that is used to protect a 400/415v 3 phase squirrel cage induction motor from overheatingdue to excessively high line currents |
overload relay |
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what type of protection is provided by ALL magnetically operated 3 phase motor starters? |
under voltage protection |
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how many line cables are required between an electromagnetic autotransformer starter and the associated squirrel cage induction motor? |
three line cables. an earth is usually required. |
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what type of 3 phase motor starter causes the motor to draw the highest starting current? |
a direct on line (DOL) starter |
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how can the direction of rotation of a 3 phase induction motor be reversed? |
By reversing any two of the incoming line leads. |
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what detirmines the thermal overload setting of a 3 phase DOL connected motor? |
The full load current of the motor. (current rating on the name plate) |
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Section 1 |
scope, application and fundamental principles |
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Section 2 |
general arrangement, control and protection |
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Section 3 |
selection and installation of wiring systems |
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Section 4 |
selection and installation of appliances and accesories |
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Section 5 |
Earthing arrangments and earthing conductors |
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Section 6 |
Damp Situations |
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Section 7 |
Special electrical installations |
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Section 8 |
testing and verification |
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in general, what is the main reason that single insulated 230v equipment be earthed? |
to ensure that the protective devices will operate in fault conditions if any exposed metallic parts come into contact with the voltage |
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Maximum values of resistance (dead) |
table 8.2 |
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Maximum values of earth fault loop impedence (live) |
table 8.1 |
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What potentially hazardous situation can arise if the MEN link is not connected correctly in an MEN installation? |
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in installation with an MENdevelops a fault whereby a person recieves an electric shock from metal water pipes. what is the most likely cause? |
open circuit or high resistance is the main neutral conductor. |
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What is the purpose of an MEN? |
This system of earthing provides a lower value offault loop impedance, allowing for faster andmore reliable operation of protection devices inthe event of a fault. |
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what is an auto transformer |
An autotransformer has a single winding with two end terminals, and one or more terminals at intermediate tap points, or it is a transformer in which the primary and secondary coils have part of, or all of their turns in common. They're smaller, lighter and cheaper than other transformers.
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Why are transformers wired in VA? |
because the power factor of the load can vary and give and give an ambiguous reading. |
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who would use a 100kVA 3 phase oil-cooled transformer |
supply authority distribution transformer |
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Transformer ratios |
N(p) V(p) I(s) ____ = ____ = ____ N(s) V(s) I(p) |
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how would you know if a transformer had shorted turns? |
Low resistance on your ohm meter |
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max resistance of the earthing conductor and the connection to a transformer? |
1 Ohm |
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what device and setting would you use to test for a short circuit between windings in a transformer? |
Insulation resistance tester set at 500Mohms |
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what can be some effects on an electrical circuit if the max safe working current is exceeded? |
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which two factors govern the value of the current that flows in a circuit if a "short circuit" occurs? |
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Safe Isolation Technique (12) |
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when providing protection in a 230v installation, what is the maximum disconnection time permissible for final sub-circuit supplying a 10A socket outlet? |
400mS 1.5.5.3 |
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when providing protection against indirect contact (fault protection), what is the maximum permissible disconnection time for a final sub-circuit supplying a fixed wire air-conditioning unit? |
5 seconds 1.5.5.3 |
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list the internal parts of an MEN |
B4.4 |
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what is SELV |
separated extra low voltage - electrically separated from earth. may not be connected to earth 7.5.5 |
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what is PELV |
protected extra low voltage - not electrically separated from earth |
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what is the main type of protection provided by RCD |
protection against phase to earth fault |
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what current will most small RCD's be set to trip at? |
30mA |
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what are two common faults that will trip RCD's? |
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what type of equipment doesn't need RCD protection? |
fixed electric cooking appliances 2.6.3.1 |
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what is the minimum number of RCD's allowed to be installed in an electrical installation? |
two. 2.6.2.4 |
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what is the maximum number of circuits that is allowed to be protected by an RCD? |
three 2.6.2.4 |
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what is the max permissible voltage drop at an 3 phase appliance in a 415v factory installation? |
5% 3.6.2 |
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what is the max permissible voltage drop at any 230v domestic installation? |
5% 3.6.2 |
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what special condition applies in relation to voltage drop in final sub-circuits which have a distributed load? |
Half the current rating of the protective device may be used. 3.6.2 |
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what are FOUR ways of reducing voltage drop in a circuit? |
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What are the THREE main ratings applied to circuit breakers? |
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what is meant by the term coordination in a circuit protection system? |
the current rating of the breaker is equal to or greater than the load rating, but equal to or less than the current rating of the cable. 2.5.3.1 |
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how will wiring systems be effected if the safe working current for a wire is exceeded? |
overheating of the wiring and magnetic stresses |
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what is the inverse time characteristic? |
the higher the fault current, the faster the trip time of the protective device |
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what limits the short circuit current when a short circuit occurs in a final sub-circuit? |
the impedance of the circuit wiring |
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what is the difference between a switch and a circuit breaker? |
a switch is manually operated, a CB is automatically operated under fault conditions. |
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is it permissible to have a mixed final sub-circuit, supplying lights and socket outlets on a construction site? |
no |
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what is the maximum length of a 2.5mm 15A extension lead on a construction site? |
40m |
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What is the maximum length of a flexible cord supplying a relocateable premises on a construction site? |
15m |
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who is responsible for classifying hazardous areas? |
the persons or parties in control of the installation. 7.7.2.1 |
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what are the two classifications for hazardous areas? |
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Name TWO of the main publications that provide outlines for testing in domestic and non domestic installations in WA |
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who is responsible for testing an installation? |
the licensed electrical worker that signs test sheets |
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list the six types of tests that must be completed before an installation is deemed safe |
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which australian standard provides specific guidelines pertaining to MEN systems and installation |
as/nzs 3017 electrical installations - verification guidelines |
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what is the maximum resistance from the earthing electrode to the main earth bar in an MEN installation? |
0.5 ohms |
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why is it essential to disconnect the equipotential bond of a hot water system before checking earth continuity |
to avoid parallel connections through water pipes. (parallel connections through water pipes could give you a lower reading) |
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what is the minimum permissible insulation resistance to earth in an installation that does not include a sheathed heating element? |
1M ohm 8.3.6.2 |
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what is the minimum permissible insulation resistance to earth in an installation that includes a sheathed heating element?
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0.01 M ohm 3.2 |
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what must you do when insulation resistance testing an installation that has multiple switching arangements like 2way and 3way switches? |
test for each switching position |
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how must a 10A socket outlet be polarised? |
Earth, active, neutral. in a clockwise direction. 4.4.5 |
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what fault would be indicated if the active and neutral tails showed 0 ohms without the supply connected? |
short circuit somewhere in the installation |
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resistance in a heating element |
R = V^2/P because P = V^2/R |
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Power Formula |
P = V^2/R
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between which points in a typical domestic installation should insulation resistance be measured? |
Between all live conductors and earth 8.3.6.1 |
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at what setting should an insulation resistance tester be set when testing a 400V 3 phase somestic installation? |
500v 8.3.6.1 |
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when testing insulation resistance, what position should the circuit switches be in? |
all switch wires must be on, otherwise you won't be testing the switch wires
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what is the major functional difference between a switch and a circuit breaker? |
a circuit breaker is usually on in the up position, whereas a switch is usually on in the down position |
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what are the main colours ona danger tag? |
red and black |
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what are the main coulours of a out of service tag? |
yellow and black |
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what is the main precaution to be taken before touching the terminals of any fixed 230v device? |
test for zero volts |
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what additional precaution should be taken before touching the terminals of a fixed device, after you've tested for zero volts? |
test the testing device on a known live source |
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who should remove the danger tag from an electrical isolator under normal working conditions? |
the person who placed it there |
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list FOUR factors which must be considered when selecting a wiring system for a particular installation |
3.1.2 |
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what is the minimum permissible current carrying capacity of the consumer mains in a single phase domestic installation? |
63A WAER 9.2.1 |
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what is the minimum permissible current carrying capacity of the consumer mains in a 3 phase domestic installation? |
32A 9.2.1 |
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what is the minimum permissable depth of underground residential consumer mains? |
500mm table 5.6 |
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where does the consumer mains begin in a domestic installation in which the consumer mains are buried under ground? |
at the termination pillar |
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what is the most important convention that must be known when reading electrical diagrams? |
all compenents are shown in the de-energised state |
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in an electrical circuit diagram shows thick lines and thun lines, what do the thick lines mean? |
usually, higher current circuits |
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what type of electrical diagram shows actual conections in individual terminals? |
wiring diagram - good for checking existing wiring in a control circuit |
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what type of electrical diagram is best for detirmining sequence of operation in a control circuit |
circuit diagram |
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hwo does OHS benefit me? |
its intended to ensure that I'm not exposed to hazards while at work |
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what does duty of care mean? |
that a person or employer has a legal obligation to take responsible care in matter relating to health and safety at the workplace. |
